<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <style>
      #dp {
        width: 0;
        height: 0;
        border: 50px solid transparent;
        border-bottom: 20px solid red;
        position: relative;
        top: -50px;
      }
      #dp:after {
        content: "";
        position: absolute;
        left: -50px;
        top: 20px;
        width: 0;
        height: 0;
        border: 50px solid transparent;
        border-top: 70px solid red;
      }
    </style>
  </head>
  <body>
    <p>两个三角形 定位</p>
    <div id="dp"></div>
  </body>
</html>
